Method of making a removable bottom for a steelmaking furnace from preformed refractory shapes

ABSTRACT

A method of making a removable bottom for a steelmaking furnace from preformed basic refractory shapes, said bottom having tuyeres for injecting gas or other material into a bottom blown steelmaking vessel and the product of the method.

nite States Patent 1 Hubble et al.

[451 Aug. 20, 1974 Inventors: David H. Hubble; John A. Lamont,

both of Westmoreland, Pa.

Assignee: United States Steel Corporation,

Pittsburgh, Pa.

Filed: June 22, 1973 Appl. No.: 372,733

Related US. Application Data Division of Ser. Nov 256,689, May 25, 1972, Pat. No. 3,799,526.

US. Cl 29/527.l, 264/30, 264/35,

Int. Cl B23p 17/04 Field of Search 29/527.1; 266/35, 36 P,

[56] References Cited UNITED STATES PATENTS 51,401 12/1865 Bessemer 266/35 256,607 4/1882 Tucker 264/30 UX 405,392 6/1889 Bertrand 1 i i. 264/30 X 556,539 3/1896 Haws 266/35 1,010,312 11/1911 Planche .1 264/30 3,070,449 12/1962 Davies et al. .4 265/30 UX 3,337,206 8/1967 Bouvier I I r 1 264/30 X 3,673,288 6/1972 Childs 264/30 X Primary Examiner-Charles W1 Lanham Assistant Examiner-D. C. Reiley, lll Attorney, Agent, or Firm-Ralph D. Dougherty [57] ABSTRACT A method of making a removable bottom for a steelmaking furnace from preformed basic refractory shapes, said bottom having tuyeres for injecting gas or other material into a bottom blown steelmaking vessel and the product of the method.

8 Claims, 12 Drawing Figures PATENTEDAus20 mm SHEET 1 BF 4 FIG.

PATENTEmuszo-mm suzzt a or 4.

Fla/2.

METHOD OF MAKING A REMOVABLE BOTTOM FOR A STEELMAKING FURNACE FROM PREFORMED REFRACTORY SHAPES This is a division of application Ser. No. 256,689, filed May 25, 1972, now US. Pat. No. 3,799,526.

In the bottom-blown oxygen steelmaking process as presently practiced, which is known as the Q-BOP process, a furnace, or vessel, has a removable bottom which contains one or more tuyeres. Oxygen and other gases or particulate matter, such as lime or other flux, is blown through the tuyeres into the vessel. The tuyeres and the surrounding refractory in the removable bottom wear during the production of steel in the vessel. Periodically, bottoms which are worn or have damaged tuyeres Heretofore, the usual method of making a removable bottom or plug for a steelmaking vessel has been to cast a mixture of dolomite and tar into a mold on a removable bottom plate. A cast plug is of relatively low density, because pressure cannot be applied during forming. Further, a cast plug cannot be prefired to sufficiently high temperatures, such as in the range of 2,000 to 3,2() F, to obtain the good properties inherent with ceramic bonding that are obtained in conventionally fired ceramic products. This is for two reasons, first the size of the plug is too large to be placed in such a furnace and secondly, the plug as cast ordinarily has metal tuyeres protruding through it which would be damaged by such high temperatures.

We have invented a method of making a removable bottom by using preformed refractory shapes of a predetermined configuration.

It is an object of our invention to provide a method of making removable furnace bottoms requiring no forming or heating equipment at the assembly site.

It is also an object to provide a method of making a furnace bottom having an extremely long operating or useful life.

It is a further object of our invention to provide a method of making a furnace bottom having higher density and greater hot strength than bottoms heretofore available, such as those made by casting of dolomitic material.

It is another object to provide a removable bottom for a bottom-blown steelmaking furnace, which bottom has a high density and high hot strength.

FIG. I is a partly diagrammatic vertical sectional view of a bottom-blown oxygen steelmaking furnace in which the bottom is made in accordance with our invention.

FIG. 2 is a plan view of the refractory plug in the bottom shown in FIG. 1.

FIG. 3 is a plan view of a modified form of bottom in accordance with our invention.

FIG. 4 is a section on line IV-IV of FIG. 3.

FIG. 5 is a plan view of another modified form of bottom in accordance with our invention.

FIG. 6 is a section on line VIVI of FIG. 5.

FIG. 7 is a plan view of still another modified form of bottom.

FIG. 8 is a section on line VIII-VIII of FIG. 7.

FIG. 9 is a plan view of yet another modified form of bottom.

FIG. 10 is a section on line X-X of FIG. 9.

FIG. I1 is a plan view of another modified form of bottom.

FIG. 12 is a section on line XIIXII of FIG. 11.

FIG. 1 shows a bottom-blown oxygen steelmaking vessel 10 which has a removable bottom 12. The bottom 12 comprises a bottom plate 14, and one or more generally upstanding tuyeres 16 (FIGS. 1, 2) which are surrounded by a refractory plug 18 (FIGS. 1, 2) and a retaining ring 19 (FIG. I), which ring 19 is upstanding from plate 14. The bottom plate 14 is fastened to the furnace 10 by bolts 20 (FIG. 1) in holes 21 (FIGS. 3, 4). The sides of the plug 18 do not contact the refractory lining 22 of the vessel, but there is sufficient clearance between the refractories 18 and 22 to permit insertion of a pitch-bearing monolithic material 24 hereinafter described or the like, which material 24 affords a metaland slag-tight seal.

According to our invention, we form the plug 18 of a plurality of high density, pitch bearing refractory shapes 25, 26, 27, and 28 (FIG. 2) having predetermined configurations placed around the tuyeres 16 leaving a minimum of open space around each tuyere 16, as shown in FIG. 2. We construct the plug 18 so that the refractory shapes 25, 26, 27 and 28 generally form the plug into the frustum of a cone or pyramid or other substantially pyramidal shape. The embodiment of FIGS. 1 and 2 is a sixtuyere plug 18 with the tuyeres 16 in a circular pattern. The central cylinder 29 (FIG. 2) is formed of six identical shapes 25. The shapes 26, 27, 28 (FIG. 2) surrounding the central cylinder 29 are solid shapes 26, and shapes 27 and 28 each of which has a hemi-cylindrical trough 30 which trough 30 forms a hole for a tuyere 16 when shapes 27 and 28 are emplaced adjacent each other. The hole is filled around the tuyere 16 with a basic monolithic refractory 24. The outermost refractory shapes 32 are placed within the retaining ring 19 to form a substantially solid plug 18. When all the refractory shapes 25, 26, 27, 28 have been installed, one or more bands 35 (FIG. 1) of steel or other material are placed on the plug 18 to prevent movement of the shapes 25, 26, 27, 28 during subsequent steps and during transportation and installation of the completed plug 18 in the furnace 10. These bands 35 are left in place permanently. The configuration of each refractory shape 25, 26, 27, 28 must be such that, after installation of the bottom 12 in the furnace l0 and heating the furnace, the refractory shapes cannot move relatively to each other when the furnace is tilted.

The refractory shapes 25, 26, 27, 28 of FIGS. 1 and 2 have vertical surfaces. Although these shapes 25, 26, 27, 28 apparently can move relatively to one another when furnace 10 is tilted, preheating of the furnace lining 22 prior to charging the furnace I0 expands the refractory shapes, whereby frictional force develops between them to hold them firmly in position relatively to one another when the furnace 10 is tilted. If desired, the shapes 25, 26, 27, 28 can be held in position by mortar between each shape. This, of course, is a more expensive method of making the bottom 12.

The exact configuration of refractory shapes used will depend on the desired arrangement of tuyeres 16 in the bottom 12. FIGS. 3 through 12 illustrate several possible alternative configurations but are not meant to limit our invention. The common features of each of the specific arrangements shown are (1) special preformed pitch-bearing basic refractory shapes, (2) a monolithic pitch-bearing basic material 24 or the like filling the voids 30 around the tuyeres I6, (3) provisions in the design to prevent movement of the preformed pitch-bearing basic refractory shapes relative to each other after the plug is installed in a bottom blown furnace, and (4) the composition of the shapes and material for filling voids 30. The absence of shape movement may be obtained by a variety of means including use of tapered or keyed shapes, interlocking shapes, tongue and groove shapes, etc. After installation of the bottom 12 in the furnace 10, a basic monolithic material 24 or the like is inserted between the plug 18 and permanent lining 22 to provide tightness as illustrated in FIG. 1.

FIGS. 3 and 4 illustrate a plug 18 formed of inverted arch bricks. The central shape 40 is a frustum of a cone. The surrounding shapes 41, 42, 43, 44 are tapered so the plug 18 acts as an arch when the furnace is inverted, preventing shape movement. The shapes 41, 42, 43, 44 can be the same length in which case the top of the plug 18 will be flat. Alternatively, the shapes 41, 42, 43, 44 can be longer nearer the periphery as shown in FIG. 4 to form a dished upper surface of the plug 18 A dished surface can be formed by emplacing a monolithic refractory material 24 or the like (not shown in FIG. 4) on bottom plate 14 to form the contour desired for the top of the plug 18 then installing equal length shapes thereon. Since shapes 41, 42, 43, 44 are positioned at an angle and tuyeres 16 are substantially vertical, hole 46 is formed through shapes 42 and 43. Monolithic refractory material 24 is inserted in each hole 46 surrounding each tuyere 16 to form a substantially solid plug 18 The embodiment of FIGS. and 6 is a IO-tuyere plug 18 Four different special shapes are used around the tuyeres 16 which are in a straight pattern. The four central shapes 50 are quadrants of a cylinder, each having a longitudinal hole 52 which enables the shape 50 to be installed on the tuyere-containing bottom plate 14 with a tuyere 16 in each hole 52. The ten shapes surrounding the central shapes 50 include four shapes 54 which are solid, four shapes 56 which have offset holes 57 and two shapes 58 which have holes 59 on their centerline. The ten outer shapes 54, 56, 58 engage retaining ring 19. Basic monolithic material 24 or the like is inserted in each hole 52, 57, 59 surrounding each tuyere 16 to form a substantially solid plug 18 The plug 18 of FIGS. 7 and 8 contains a large central solid shape 65 which is the frustum of a cone. A number, for example six, of tapered intermediate shapes 66 form a solid cylinder with shape 65. Tuyeres 16 are arranged in a circular pattern in void 68 between shapes 66 and tapered outer shape 69 disposed outside the shapes 66. The tapered outer shapes 69 are notched at 70 to engage retaining ring 19. Basic monolithic material 24 or the like is placed in the void 68 between shapes 66 and 69 to form a solid plug 18 The plug 18 of FIGS. 9 and include a central cylindrical shape 72 surrounded by a number of intermediate shapes 73. Each-of the shapes 73 abuts a tapered shape 74. A pair of intermediate shapes 73 and their abutting pair of outer shapes 74, each of which shape has a recessed quarter-cylindrical hole, which holes form a hole 75 for a tuyere 16. The hole 75 is then filled with a basic monolithic material 24 or the like to form a substantially solid plug 18. Band 35 is placed around the plug 18 prior to emplacement in furnace 10.

FIGS. 11 and 12 illustrate a plug l8 formed of interlocking shapes 80, 81, 82, 83. Central cylinder 80 has a groove 84 (FIG. 12). Each surrounding intermediate shape 81 has an inward projection 85 which engages groove 84 in cylinder and a groove 86 in its outer surface to receive a similar projection 87 from a shape 82 in the next course. Outer tapered shapes 83 have inward projections 88 (FIG. 12) which engage a groove 89 in the outer surface of shapes 82. Tuyeres 16 extend through suitable holes 90 in shapes 82 and the void therebetween is filled with a basic monolithic material 24 or the like in the same manner as FIG. 5.

Tuyeres may extend through one or more shapes as in FIGS. 5 and 6, they may be positioned between rows of shapes as in FIGS. 7 and 8, at the point of communication of four or more shapes as in FIGS. 9 and 10, at the interface of two bricks as in FIGS. 1 and 2, or any combination thereof. Tuyeres can be perpendicular to the bottom plate or at an angle thereto. Of course, the assembly of the plug becomes more difficult as the angle of inclination of the tuyere increases from normal.

PLUG MATERIAL The preformed pitch-bearing basic refractory shapes shown in FIGS. 1-12 may be of the pitch-bonded tempered (baked) or pitch-impregnated types in magnesite or dolomite composition (or combinations thereof). While the refractory composition is not limited, the following table shows the properties of the preferred materials which should be used to insure service perform- Our tempered refractory shapes (FIGS. 1-12) are made of a mixture of a basic refractory aggregate such as magnesite or dolomite or both, high temperature pitch and fine carbon. Magnesite is defined as magnesium oxide derived from naturally occurring carbonates or hydroxides, or derived synthetically from sea water or brine. Dolomite is defined as a mixture of calcium and magnesium oxides derived from naturally occurring carbonates. Our magnesite has a composition of about to 98% MgO (on the pitch free basis) and preferably about 94 to 96% MgO. Dolomite has a composition of about 38 to 45% MgO, with the balance substantially lime. Both magnesite and dolomite are fired to a temperature of above 3,000 F to drive off gases and to produce a dense stable product. The density of this product is defined by its grain porosity. For our application, the grain porosity (i.e., pore volume) of the magnesite or dolomite must be less than 12% of total volume and preferably less than 8%. The silica content of the refractory aggregate must be no greater than 3.0%. A higher silica content will reduce the melting point of the refractory, increasing the wear rate of the plug. The total R 0 content of the dolomite must be limited to 1% maximum. R 0 can be iron oxide,

aluminum oxide, chromic oxide or boric oxide or the like. These oxides act as a flux on the dolomite and will cause a breakdown of the refractory, increasing the wear rate. Higher R 0 contents can be tolerated in magnesite because it has a higher MgO content. The magnesite or dolomite must be sized in a manner to obtain the maximum product density, but must all be 3 mesh.

Fine carbon such as lampblack, fine coke, or fine graphite is mixed with the basic refractory aggregate and preheated to a temperature of 300 to 600 F. The particle size of the fine carbon must be l00 mesh, and preferably should be 325 mesh. About 85 to 95 parts of magnesite are mixed with 0.5 to 4.0 parts of fine carbon, but we prefer 92 to 94 parts of magnesite and 1 V2 to 2% parts fine carbon.

Pitch having a ring and ball softening point in the range from 150 to 285 F and preferably in the range of 185 to 230 F is preheated to from 50 to 200 F above its softening point. We mix from 2 to 8 parts of pitch with the previously formed refractory aggregate carbon mixture to form a moldable mass. Preferably about 2 to 6 parts of pitch are employed in the mixture. The pitch should have a Quinoline Insoluble fraction ranging from 8 to 17%.

The thoroughly mixed moldable mass is maintained at a temperature of from 50 to 200 F above the softening point of the pitch while it is pressed into a mold to form the desired shape. When pressing is completed, the shape is placed in a muffle oven, baked at a temperatureof from 350 to 800 F for a period of from 2 to 100 hours. The preferred baking temperature is from 500 to 600 F, and the preferred baking time is from 6 to 60 hours. In a muffle-type furnace, the pitch volatiles, which are driven off, are retained in the region surrounding the plug to form a reducing atmosphere, thus avoiding oxidation by exposure of the bottom to oxidizing gases.

Our burned-impregnated refractory shapes are of a mixture of a basic refractory aggregate such as magnesite or dolomite, or both, and a high temperature pitch which is subsequently injected into the pores or the brick by vacuum impregnation. The magnesite and dolomite for the impregnated brick has the same composition, density, sizing and other restrictions as defined above for the tempered brick. This refractory material is pressed with a temporary chemical binder, then fired to a temperature above 2,800 F for at least 30 minutes to form the desired refractory shape. After firing, the shape is placed in a vacuum impregnation chamber and pitch is forced into the pores of the shape. Pitch having a ring and ball softening point from 120 to 250 F, and preferably in the range of 160 to 220 F is used to impregnate the shape.

MONOLITHIC MATERIAL 24 The pitch-bearing basic monolithic material 24 (FIGS. 1-12) to be placed in the space between the preformed shapes and tuyeres may be either a waterbased pitch-bearing material or a mixture of pitch or tar with sized magnesite and dolomite.

Our water-based, pitch-bearing basic refractory monolithic material is made of a mixture of magnesite, high-temperature pitch, fine carbon and a watersoluble chemical bonding agent. Our magnesite has a composition of from 90 to 98% MgO and preferably about 94 to 96% MgO. The magnesite is fired to a temperature above 3,000 F to drive off gases and to produce a dense stable product. The density of this product is defined by its grain porosity. For our application, the grain porosity (i.e., pore volume) of the magnesite must be less than 12% of its total volume and preferably less than 8%. The silica content of the magnesite must be limited to less than 3%. A higher silica content will reduce the melting point of the monolithic refractory material, increasing the wear rate of the material after installation. The magnesite must be sized in a manner to obtain the maximum product density, but should all be 3 mesh.

We prepare a mixture of:

a. about to and preferably 90 to 93% magnesite;

b. about 1 to 5% and preferably 1 /2 to 2 /2% fine carbon, such as lamp black, fine coke, or fine graphite;

c. about 2 to 8% and preferably 3 to 5% ground pitch; and

d. about 1 to 8% and preferably 2 to 5% water soluble chemical bonding agent such as chromic acid, sodium silicate, magnesium chloride, magnesium sulfate, or boric acid.

The particle size of the fine carbon and ground pitch must be'-100 mesh, and preferably should be 325 mesh to obtain uniform distribution throughout the product.

Any suitable pitch which has a ring and ball softening point in the range of 210 to 300 F and preferably in the high end of the range may be used, including but not limited to petroleum pitch, coal tar pitch and the like. The water soluble chemical binder can be added in dry powder form or premixed with water. The monolithic material may be cast or rammed into the space around the tuyeres in a manner to obtain the best possible density.

Our alternative monolithic material 24 (FIGS. 1-12) is a pitch or tar refractory mixture made of a mixture of magnesite and/or dolomite, and pitch having a ring and ball softening point from 60 to 250 F. Optionally, fine carbon may be added to this mixture. The magnesite and dolomite requirements are those described above. The mixture comprises 85 to 98% refractory aggregate, 2 to 15% pitch, and 0 to 5% fine carbon. This mixture may be placed around the tuyeres cold or it may be preheated to liquify the pitch.

The amount of space left around each tuyere shall be the minimum consistent with practical considerations for a particular tuyere arrangement (i.e., from 0 to 3 inches.) Although it is possible for shapes to be so closely fitted around the tuyeres that no monolithic material would be required, size tolerances for the shapes, size of tuyeres, tuyere locations, and other practical considerations make this impossible in nearly all cases. There is no requirement that the tuyere be centered in the space.

As a specific example, we made a plug 18 from burned-impregnated magnesite brick in the general design illustrated in FIGS. 1 and 2. This impregnated magnesite brick had a composition on a pitch-free basis of 95.2% MgO, 2.8% CaO, 1.3% SiO 0.4% Fe O and 0.3% A1 0 The bulk density of the preformed shapes 25, 26, 27, 28 used averaged lbs/cu. ft., the residual carbon content was 2.2%, and the modulus of rupture at 2,700 F was 1,250 psi.

These shapes 25, 26, 27, 28 were installed on a bottom plate 14 around the tuyeres l6 and steel bands 35 were applied. A pitch-bearing monolithic material 24 consisting of a mixture of 92% magnesite and 8% of a 150 F softening point pitch was then rammed into the approximately /2 inch wide space 30 between the tuyeres l6 and surrounding preformed shapes 27, 28. The assembled plug 18 was installed in the bottom of a 40-ton experimental Q-BOP vessel 10 which was operated intermittently for 46 heats. The plug 18 had a wear rate of about 0.16 inch per heat.

It is readily apparent from the foregoing that we have invented a method of making a removable bottom for a bottom blown steelmaking process which method requires no forming or heating equipment at the assembly site and which resulting bottom has high density, high hot strength and a long operating life.

We claim:

1. A method of making a tuyere-containing removable bottom for a steelmaking furnace comprising:

installing on a metal bottom plate containing a generally upstanding tuyere fixed thereto, a plurality of pitch-bearing refractory shapes having a predetermined configuration to form a substantially solid plug leaving only a minimum of open space around each tuyere, and

filling said space around each tuyere with a pitchbearing monolithic material.

2. A method according to claim 1 further comprising installing a metal band around said plug above said bottom plate and substantially parallel thereto, whereby movement of any shape relatively to any other shape is prevented.

3. A method according to claim 1 wherein said plug is frusto-conical in shape.

4. A method according to claim 1 wherein said plug is frusto-pyramidal in shape.

5. A method according to claim 1 wherein said shapes consist essentially of tempered magnesite, and have a bulk density greater than 185 lbs/cu. ft. and a residual carbon content greater than 4%.

6. A method according to claim 1 wherein said shapes consist essentially of tempered dolomite, and have a bulk density greater than lbs/cu. ft. and a residual carbon content greater than 4%.

7. A method according to claim 1 wherein said shapes consist essentially of burned-impregnated magnesite, and have a bulk density greater than lbs/cu. ft, a residual carbon content greater than 2% and a modulus of rupture at 2,700 F greater than 1,000 lbs/sq. in.

8. A method according to claim 1 wherein said shapes consist essentially of burned-impregnated dolomite, and have a bulk density greater than lbs/cu. ft., a residual carbon content graater than 1.5% and a modulus of rupture at 2,700 F greater than 800 psi.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO. 3,829,960 Dated Au st '20, 197

) David Hubble et a1.

Inventor(s v It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Correct the attorney of record's name from "Ralph D. Dougherty" to Ralph H. Dougherty Column 1, line 16, after "tuyeres insert must be removed from the vessel and replaced between heats.

Column 3, line 50, after "between" insert center Column 5, line 42, after- "pores" change "or" to of (In applicatiomt signed am seatefithis 19t of Nwefiber 1974' (SEAL) Attest:

MCCOY GIBSQN JR c. MARSHALL DANN v Attestlng Off1cer Commissioner of Patents uscoMM-oc scan-Pee U.4 GOVEKNHENT'PRHH 'HCG OFFICE:

FORM Po -1050 (IO-69)- 

1. A method of making a tuyere-containing removable bottom for a steelmaking furnace comprising: installing on a metal bottom plate containing a generally upstanding tuyere fixed thereto, a plurality of pitch-bearing refractory shapes having a predetermined configuration to form a substantially solid plug leaving only a minimum of open space around each tuyere, and filling said space around each tuyere with a pitch-bearing monolithic material.
 2. A method according to claim 1 further comprising installing a metal band around said plug above said bottom plate and substantially parallel thereto, whereby movement of any shape relatively to any other shape is prevented.
 3. A method according to claim 1 wherein said plug is frusto-conical in shape.
 4. A method according to claim 1 wherein said plug is frusto-pyramidal in shape.
 5. A method according to claim 1 wherein said shapes consist essentially of tempered magnesite, and have a bulk density greater than 185 lbs/cu. ft. and a residual carbon content greater than 4%.
 6. A method according to claim 1 wherein said shapes consist essentially of tempered dolomite, and have a bulk density greater than 175 lbs./cu. ft. and a residual carbon content greater than 4%.
 7. A method according to claim 1 wherein said shapes consist essentially of burned-impregnated magnesite, and have a bulk density greater than 180 lbs./cu. ft, a residual carbon content greater than 2% and a modulus of rupture at 2,700* F greater than 1,000 lbs./sq. in.
 8. A method according to claim 1 wherein said shapes consist essentially of burned-impregnated dolomite, and have a bulk density greater than 190 lbs./cu. ft., a residual carbon content graater than 1.5% and a modulus of rupture at 2,700* F greater than 800 psi. 